I just experienced the AY J seat and can’t say I am a fan.
The first leg was Haneda to Helsinki, which was a 13 hour flight leaving at 21:50.
Having just got off a 10 hour QF flight on an A330 I was pretty tired, so no meal, just a beer and then settled down.
In 3L the feet space was just too thin. I am a restless sleeper so toss and turn. My feet were just banging into the end of the seat or that rotten pole. And although I’m 6 foot, I reckon a taller Finnish person would be jammed in at each end when lying at full stretch.
The hardness of the seat and leg area really shows up when you are trying to sleep - there is no give at all.
As noted by Lynda, the mattress topper is just placed on the top. I managed to roll it into a ball along with the pillow case.
The seat belt also retracts and tends to lock you in.
The next flight was a day flight of 2 hours. For this I did enjoy the seat. I find the QF seat to be a pain to try to set up for a recline with my legs supported. Being able to curl my legs up without hitting any hardware was good.
7/10 for me.